MOIRCS Information for Spectroscopy Mode



OPE File Information

Please read the following documents before your observation.

    Sample OPE file for spectroscopy observation can be downloaded here. (Last update 2024-03-07)

      The appearance may be strange with no line break under the Windows browser -- you may change .ope to .txt if it happens.

      Edit the following lines suggested as ">>> To Users:" in the ope file and send back to the primary SA beforehand. You don't have to care too much about the detail of the numbers (exposure time, dither length, etc). They will be adjusted on site.

    Observing Time Table Template is also available here.

      Sharing the plan is very important for better understanding of your plan among the observing staff. Fill it and send back to the Support Staff before your observing run starts.

  • Description of the OPE file: Guide to MOS Observation with MOIRCS [Under Construction]
  • The list of the current filter and grism configuration alias can be found here (Last update: 2024-03-05)
  • Recent dome flat setting log can be found here (internal only).

Flat Fielding/Comparison

We used to use a bare aluminum back surface of the top screen for the dome flat surface until July 2020. Then we updated the dome flat surface to a better quality panels (Parmaflect-94). All the dome flat data after August 2020 has been under the new (and better) dome flat panel.

Dome flat data will be taken before and after the observation. As a default we take 7 dome flat data for each mask. We will also take the lamp-off dome flat data for the spectroscopy observation in the K-band window (HK500 & VPH-K). We usually do not take the lamp-off dome data for the other wavelengths, because it is not essential. Instead, the Dark data under the same exposure will be provided to uses for the hot pixel subtraction purpose. If you need the lamp-off data for YJH spectroscopy, please explicitly request it before the observation.

The Halogen Lamp on the calibration probe may also work as a flat field data, though it can illuminate only a part of the field of view. We take the flat data at least on 5 cal-probe position in order to illuminate the whole MOS area. Still, the uniformity of the light across the field of view will be lost once we move the cal probe. An advantage of Halogen lamp is that there is no absorption between the atmospheric windows (between Y/J/H/K).

The ThAr comparison lamp is available for the wavelength calibration. We take the comparison data by scanning the entire MOS field of view (namely take exposures at the 4-5 position). As there are many OH night sky lines available for the NIR window, we recommend to use the OH lines for calibration for medium-resolution spectroscopy. But there are some wavelength region where the OH line is relatively poor (e.g. red side of K window). The night lines may also be blended in the low-dispersion grism (zJ500, HK500) data, especially in YJ window. Therefore, we take the ThAr data for the R500 observation. Be aware that the slit mask position between the science data and the calibration data may be slightly different, which may introduce the systematic error during wavelength calibration. You can check the possible shift by comparing the mask image during the obs and calibration. For more detail, see the Wavelength calibration page.


Autoguider Issue

As the MOIRCS FOV occupies a large fraction of the Cassegrain field of view, the area we can choose an Auto Guider (AG) star without vignetting is fairly limited. A star with visual magnitude of 9 to 16 in the R-band (650 nm) is necessary as the AG star. Such bright stars are relatively sparse in high Galactic latitude, and sometimes it is difficult to find such a star in the non-vignetting area. If the AG vignetting in the imaging data occurs, it would complicate the data reduction. Also in MOS mode, you may lose the data from some slitlets by vignetting. To avoid such troubles, all MOS (or NB119 imaging too) observers should check the availability of an AG star in the "safe" area before the observation to avoid the possible loss of important targets.

The diameter of the shadow by the Autoguider has 72 arcseconds. You can choose any bright star within a 4.6'-radius area from the FOV center in the Cassegrain focal area (See figure below). But if you want to avoid vignetting by the shadow of the AG probe, the area you can choose is limited to at least 72" away from the edge of the MOIRCS f.o.v. or any of your slitlets. The blue-colored area in the bottom figure indicates the "safe" region, where the shadow of the AG probe will never cause vignetting on the area you may put slitlets. For imaging, only the left and the right side of the blue areas can be used for the AG.


The ds9 region file for the AG availability check is available here. It is prepared for the DSS image only.

Another issue is the effect of the Moon, cloud, or twilight onto the AG. As is written in the Imaging Information page, the AG may not work properly if the Moon is close to your target less than 20 degrees. And also, the autoguider may quickly lose the star if cirrus/clouds come into the field of view during the bright nights. Once we completely lose the AG star, the MOS alignment will be lost. As the MOS alignment takes long (>20 min), it is not recommended to push the spectroscopic observation under cloudy condition. The twilight in morning time will also change the background level very quickly and the AG will become unavailable. Usually we ask to take preimaging data during the morning time.



Troubled Data Information

The list below is not complete. The use of any archived data should be with enough caution. The date is in HST.

Before the MOIRCS Upgrade


MOS Spectroscopic Data Reduction Software



If you are developing your own software and want to put the link to your software website here, please contact to the SA. We greatly appreciate your contribution.



Please note that all data on these pages are subject to change. Any questions/comments should be directed to the SA (Ichi Tanaka: ichi [at] subaru.naoj.org ; change " [at] " to @).

Updated 2024-3-5


Copyright © 2000-2024 Subaru Telescope, NAOJ. All rights reserved.